Methods and devices for measuring raman scattering of a sample

ABSTRACT

This invention relates to a light delivery and collection device for measuring Raman scattering from a large area of a sample. The light delivery and collection device comprises a reflective cavity made of a material or having a surface coating with high reflectivity to the excitation light and the Raman scattered light. The reflective cavity has two apertures. The first aperture is configured to receive the excitation light which then projects onto the second aperture. The second aperture is configured to be applied close to the sample such that the reflective cavity substantially forms an enclosure covering a large area of the sample. The excitation light produces Raman scattered light from the covered area of the sample. The reflective cavity reflects any excitation light and Raman light scattered from the sample unless the excitation light and the Raman scattered light either emit from the first aperture to be measured with a spectrometer device, or are re-scattered by the sample at the second aperture. The multi-reflection of the reflective cavity greatly improves the excitation efficiency of Raman scattering from the sample and in the meantime enhances its collection efficiency. In addition, it also causes more excitation light to penetrate into a diffusely scattering sample and allows efficient collection of the Raman scattered light generated thereof, hence enabling sub-surface Raman scattering measurement.

FIELD OF THE INVENTION

This invention generally relates to a light delivery and collectiondevice, and more specifically to a light delivery and collection devicefor measuring Raman scattering of a sample.

BACKGROUND

Raman spectroscopy is an optical spectroscopy technique, which measuresthe inelastic scattering, i.e. Raman scattering of monochromatic lightby a material to produce a spectrum characteristic of the material.Raman spectroscopy has been demonstrated to be a powerful non-invasiveanalytical technology for material characterization and identification.

Conventional Raman spectroscopy generally utilizes a well-focused laserbeam to produce Raman scattering signal from the sample. This approachhas the apparent advantage of relatively high efficiency in Raman signalexcitation and collection. However, it also suffers from the followingdrawbacks. First, only a small volume of the sample is measured. Thusthe collected Raman spectrum may not be very representative, especiallyfor some non-uniform samples. Second, the tightly focused laser beam maycause damage to some delicate samples. Third, for diffusely scatteringsamples which are not transparent to the laser beam, this approach willonly measure the Raman scattering signal from the surface layer of thesample. The majority of the material underneath the surface will bealmost completely out of reach. There thus exists a need for an improvedlight delivery and collection device for performing Raman spectroscopy,which not only allows the measurement of a large area of the sample butalso enables sub-surface Raman signal excitation and collection.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a light deliveryand collection device for measuring Raman scattering from a large areaof a sample. The light delivery and collection device comprises areflective cavity made of a material or having a surface coating withhigh reflectivity to the excitation light and the Raman scattered light.The reflective cavity has two apertures. The first aperture isconfigured to receive the excitation light which then projects onto thesecond aperture. The second aperture is configured to be applied closeto the sample such that the reflective cavity substantially forms anenclosure covering a large area of the sample. The excitation lightproduces Raman scattered light from the covered area of the sample. Thereflective cavity reflects any excitation light and Raman lightscattered from the sample unless the excitation light and the Ramanscattered light either emit from the first aperture to be measured witha spectrometer device, or are re-scattered by the sample at the secondaperture. The multi-reflection of the reflective cavity greatly improvesthe excitation efficiency of Raman scattering from the sample and in themeantime enhances its collection efficiency. In addition, it also causesmore excitation light to penetrate into a diffusely scattering sampleand allows efficient collection of the Raman scattered light generatedthereof, hence enabling sub-surface Raman scattering measurement.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages allin accordance with the present invention.

FIGS. 1A-C illustrate a first exemplary embodiment of the light deliveryand collection device having a reflective cavity for Raman scatteringexcitation and collection as well as a receptacle for receiving a probe;

FIG. 2 illustrates a second exemplary embodiment of the light deliveryand collection device having a reflective cavity for Raman scatteringexcitation and collection as well as a receptacle for receiving anoptical fiber or fiber bundle;

FIG. 3 illustrates a variation of the first exemplary embodiment of thelight delivery and collection device, which has a differently shapedreflective cavity;

FIG. 4 illustrates a scheme of utilizing the first exemplary embodimentof the light delivery and collection device for measuring thetransmissive Raman scattering of a diffusely scattering sample;

FIG. 5 illustrates a slightly different scheme of utilizing the firstexemplary embodiment of the light delivery and collection device formeasuring the transmissive Raman scattering of a diffusely scatteringsample;

FIGS. 6A-D show the measured Raman spectrum of a sodium benzoate samplecontained in a plastic bottle, as well as the Raman spectrum of theplastic bottle and the Raman spectrum of the sodium benzoate sample forcomparison;

FIGS. 7A-C show the measured Raman spectrum of a D(+)-Glucose samplecontained in a brown envelope, as well as the Raman spectrum of thebrown envelope and the Raman spectrum of the D(+)-Glucose sample forcomparison; and

FIGS. 8A-C show the Raman spectrum of a coated ibuprofen tablet sampleobtained in three different measurement modes.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

DETAILED DESCRIPTION

Before describing in detail embodiments that are in accordance with thepresent invention, it should be observed that the embodiments resideprimarily in combinations of method steps and apparatus componentsrelated to a light delivery and collection device for measuring Ramanscattering of a sample. Accordingly, the apparatus components and methodsteps have been represented where appropriate by conventional symbols inthe drawings, showing only those specific details that are pertinent tounderstanding the embodiments of the present invention so as not toobscure the disclosure with details that will be readily apparent tothose of ordinary skill in the art having the benefit of the descriptionherein.

In this document, relational terms such as first and second, top andbottom, and the like may be used solely to distinguish one entity oraction from another entity or action without necessarily requiring orimplying any actual such relationship or order between such entities oractions. The terms “comprises,” “comprising,” or any other variationthereof, are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus. An element proceeded by “comprises . . . a” does not, withoutmore constraints, preclude the existence of additional identicalelements in the process, method, article, or apparatus that comprisesthe element.

FIG. 1a illustrates a first exemplary embodiment of the light deliveryand collection device, which is configured to deliver excitation lightto a large area of a sample and collect the Raman scattered lightgenerated thereof. The light delivery and collection device 100comprises a reflective cavity 102 which is made of a material with highreflectivity to the excitation light and the Raman scattered light. Suchmaterial can be metal materials, e.g. gold, silver, copper, andaluminum, etc. Or it can be dielectric materials, preferably particlesof dielectric materials which are firmly packed together. The dielectricmaterial is transparent or translucent to the excitation light and theRaman scattering light and reflects the light through multiplereflection at the boundary of the particles or through diffusescattering inside the translucent material. The surface of thereflective cavity is preferably polished to increase its reflectivity.Alternatively, the reflective cavity 102 may have a surface coating withhigh reflectivity to the excitation light and the Raman scattered light.Such surface coating can be a metal coating which exhibits highreflection in a broad range of wavelengths. Or it can be a dielectriccoating, which has a customized reflection wavelength range. The latterone may reflect only the wavelengths of interest thus rejecting straylight or fluorescence light which does not overlap with the excitationlight and the Raman scattered light in wavelength.

The light delivery and collection device 100 further comprises areceptacle 118 which is configured to receive a probe 120. The probe 120comprises one or more optical components 122, such as optical lenses,mirrors, filters, beam splitters, optical fibers, etc., which receiveexcitation light from a light source, such as a laser light source (notshown) and focus the excitation light at a first aperture 104 of thereflective cavity 102 and thereby deliver the excitation light 114 intothe reflective cavity 102. The aperture 104 preferably has a size assmall as possible, but large enough to pass unobstructed the excitationlight and Raman light collectable by the probe 120. The excitation light114 diverges and projects onto a second aperture 106 of the reflectivecavity 102, which preferably has a size much larger than the firstaperture 104, and more preferably, at least 2 times as large as thefirst aperture 104 in area and covering an area of at least a few squaremillimeters. The second aperture 106 of the reflective cavity 102 isconfigured to be applied close to the sample 108 such that thereflective cavity 102 substantially forms an enclosure covering a largearea of the sample 108, where the excitation light 114 produces Ramanscattered light 116 from the covered area of the sample 108. Bycollecting the Raman scattering from a large volume of the sample, theexcitation light intensity on the sample is reduced to avoid sampledamage. In the meantime, the collected Raman spectrum is morerepresentative, especially for non-uniform samples. Here the sample 108can be diffusely scattering samples, such as pharmaceuticals, powders,biological tissues, etc. or even samples having multiple layers ofdifferent materials. In the example as shown in FIG. 1 a, the sample 108is a diffusely scattering sample having a surface layer 110 and asub-surface layer 112, e.g. a container with powders inside. The sample108 scatters the excitation light 114, either through elastic scatteringor inelastic scattering, i.e. Raman scattering back into the reflectivecavity 102. The reflective cavity 102 reflects any excitation light andRaman scattered light scattered from the sample unless the excitationlight and the Raman scattered light either emit from the first aperture104 to be collected by the probe 120 and then measured with aspectrometer device (not shown) to obtain a Raman spectrum of the sample108, or are re-scattered by the sample 108 at the second aperture 106.The multi-reflection of the reflective cavity greatly improves theexcitation efficiency of Raman scattering from the sample and in themeantime enhances its collection efficiency. In this example, theexcitation light 114 penetrates through the surface layer 110 of thesample 108 with the aid of the reflective cavity 102 and produces Ramanscattering from the sub-surface layer 112 of the sample 108. Hence themeasured Raman spectrum contains the characteristic information of boththe surface layer 110 and the sub-surface layer 112 of the sample 108.In a separate step, the light delivery and collection device 100 can beremoved and the excitation light from the probe 120 is directly focusedonto the surface layer 110 of the sample 108 to measure a Raman spectrumof the surface layer 110. The latter Raman spectrum can bemathematically extracted from the previously measured Raman spectrum toobtain a Raman spectrum of the sub-surface layer of the sample. Theenhanced excitation and collection efficiency of the Raman scatteredlight as provided by the reflective cavity hence enables sub-surfaceRaman scattering measurement.

Optically, the reflective cavity serves three purposes, including (i) toprovide a large sampling area; (ii) to maximize signal collection bymeans of multiple reflection and scattering as explained previously; and(iii) to isolate the sampled area from ambient light which wouldotherwise contaminate the signal. The size of the sampling area shouldbe determined by the specific sampling requirement. For example, if thesample is heterogeneous and the goal is to obtain a betterrepresentation of the sample in whole, the sampling area should be madeat least several times larger than the grain size. If the purpose is tomeasure sub-surface sample through a layer of packaging material, thenthe linear size of the sampling area should be several times thethickness of the packaging material. With the desired sampling areadetermined, FIG. 1b further illustrates the design considerations of thereflective cavity to achieve maximum signal collection. The excitationlight beam 114 from the probe 120 is focused by the optical components122 at the first aperture 104, and then diverges and projects onto thesecond aperture 106, covering an initial illumination area 130. Thelight beam 116 collectable by the probe optics similarly projects acollection area 132. The collection area 132 and the initialillumination area 130 may be different in size. With the probe opticsfixed, the minimum size of the first aperture 104 and the divergenceangles of both beams are determined. For maximum collection efficiency,the size of the first aperture 104 should be made as small as possiblewithout obstructing the excitation and collection beams, that is, justlarge enough to encircle their beam waists at the first aperture 104. Ifit is made much larger, scattered excitation light and Raman lightfalling on the area outside the collection beam waist but inside thefirst aperture will exit the first aperture 104 without being collectedby the probe 120. To determine the size of the second aperture 106 formaximum signal collection, one shall first consider that the lightoutside the aperture is blocked, so the aperture should be at least thesize of the desired sampling area. Next the inevitable loss at eachreflection by the reflective cavity 102 and at each scattering by thesample 108 must be considered. For maximum collection efficiency, theRaman scattered light should be allowed to exit the first aperture 104and to be collected by the probe 120 by going through as few rounds ofreflection and scattering as possible. If the second aperture 106 ismade larger than the projected area 132, Raman light emerging from thearea outside the projected area 132 cannot be captured by the probe 120without going through more reflection and scattering, which will resultin reduced efficiency and limit the effective sampling area to area 132.Therefore the sampling area is the smaller of area 132 and the secondaperture 106. On the other hand, the angle of collection 134 as shown inFIG. 1c for signal light from the second aperture 106 is proportional tothe collection beam size at the first aperture 104, and inverselyproportional to the cavity length. The larger this angle is, the higherthe collection efficiency. Therefore, the cavity length should be madeas short as possible, without reducing the projected area 132 to belowthe required sampling area. These factors combine to provide that foroptimal efficiency, the size of the second aperture 106 should be equalto the desired sampling area, and that the cavity length should be suchthat the projected area 132 is equal to the size of the second aperture106.

Preferably, the second aperture 106 of the reflective cavity 102 is atleast 2 times as large as the first aperture 104 in area.

FIG. 2 illustrates a second exemplary embodiment of the light deliveryand collection device. Here the light delivery and collection device 200comprises a reflective cavity 202 having a similar structure as thereflective cavity 102 in FIG. 1, as well as a receptacle 218 which isconfigured to receive one or more optical fibers or fiber bundles 220.The optical fiber or fiber bundle terminates at the proximity of a firstaperture 204 of the reflective cavity 202 so as to deliver theexcitation light from a light source (not shown) into the reflectivecavity 202. In a similar way as shown in FIG. 1, the excitation light214 excites Raman scattering from the sample 208 at a second aperture206 of the reflective cavity 202. The reflective cavity 202 reflects anyexcitation light and Raman scattered light 216 scattered from the sampleunless the excitation light and the Raman scattered light 216 eitheremit from the first aperture 204 to be collected by the fibers 220 andthen measured with a spectrometer device (not shown) to obtain a Ramanspectrum of the sample 208, or are re-scattered by the sample 208 at thesecond aperture 206. The fiber bundle 220 may comprise multiple opticalfibers 222. A portion of the fibers, e.g. the fiber in the center of thebundle may be used for delivering the excitation light while the otherportion of the fibers, e.g. the fibers at the periphery of the bundlemay be used for collecting the Raman scattered light.

The reflective cavity of the light delivery and collection device maytake different shapes. In a slight variation of the light delivery andcollection device as shown in FIG. 3, the reflective cavity 302 of thelight delivery and collection device 300 is spherically or paraboloidalshaped. The special shape may favorably reflect the light into certaindirections hence increasing the excitation and collection efficiency ofthe Raman scattering in those directions.

In yet another variation of the light delivery and collection device,the reflective cavity may have an additional aperture for outputting theRaman scattered light. The position of this aperture on the reflectivecavity may be optimized, for example, to minimize the collectedpercentage of the Raman scattering signal from the surface material ofthe sample and maximize the collected percentage of the Raman scatteringsignal from the sub-surface material of the sample. Alternatively, theadditional aperture may be used to deliver another excitation light ofdifferent wavelength to excite Raman scattering from the sample.

FIG. 4 illustrates a scheme of utilizing the first exemplary embodimentof the light delivery and collection device for measuring thetransmissive Raman scattering of a diffusely scattering sample. In thisexample, two of such devices are utilized. One device is used fordelivering the excitation light to one side of the sample and anotherdevice is used for collecting the Raman scattered light from theopposite side of the sample. Referring to FIG. 4, the light deliverydevice 400 has a receptacle 418 to receive a probe 420 and a reflectivecavity 402 with its first aperture 404 in communication with the probe420 to receive the excitation light 414. The second aperture 406 of thelight delivery device 400 is applied close to one side of the sample 408such that the reflective cavity 402 of the light delivery device 400substantially forms an enclosure covering a large area of the sample toexcite Raman scattered light 416 thereof. The light collection device430 has a reflective cavity 432 with its second aperture 436 appliedonto the opposite side of the sample 408 such that the reflective cavity432 collects the Raman scattered light that transmits through the sample408 and delivers it through the first aperture 434 of the reflectivecavity 432 to a probe 440 to be analyzed by a spectrometer device (notshown). The reflective cavity 402 of the light delivery device 400enhances the Raman excitation and collection efficiency by reflectingback into the sample the majority of excitation light and Ramanscattered light that are scattered back by the sample until theytransmits through the sample. The reflective cavity 432 of the lightdelivery device 430 functions similarly by reflecting back anyexcitation light and Raman scattered light that do not fall on its exitaperture, i.e. the first aperture 434. In a slight variation of thepresent scheme, the light delivery device 400 may also be used forcollecting the back scattered Raman light from the sample 408 in asimilar way as shown in FIG. 1. The spectrum of the back scattered Ramanlight and the forward scattered Raman light may be used together toanalyze the composition of the sample 408.

FIG. 5 illustrates a slightly different scheme of utilizing the firstexemplary embodiment of the light delivery and collection device formeasuring the transmissive Raman scattering of a diffusely scatteringsample. Here the excitation light 514 is directly delivered onto oneside of the sample 508 to excite Raman scattered light 516 from thesample. The excitation light 514 can be either collimated, orconverging, or diverging. A light collection device 530 with similardesign as shown in FIG. 1 is employed to collect the Raman scatteredlight 516 that transmits through the sample 508.

In a similar manner, the light delivery and collection device as shownFIG. 2 and FIG. 3 may be used for measuring the transmissive Ramanscattering of transparent or diffusely scattering samples.

FIG. 6 and FIG. 7 show two examples of utilizing the light delivery andcollection device for measuring the Raman spectra of diffuselyscattering samples contained in diffusely scattering containers.

FIG. 6a shows the Raman spectrum of sodium benzoate powder contained ina white plastic bottle, which is measured with the aid of a lightdelivery and collection device as shown in FIG. 1. FIG. 6b shows themeasured Raman spectrum of the plastic bottle by removing the lightdelivery and collection device and focusing the laser beam directly onthe surface of the plastic bottle. By properly scaling the spectrum inFIG. 6b and then subtracting the scaled spectrum from the spectrum inFIG. 6a , one can obtain a calculated Raman spectrum of the sodiumbenzoate powder as shown in FIG. 6c . Comparing this spectrum with theRaman spectrum shown in FIG. 6d , which is collected directly frompurely sodium benzoate powder, it can be seen that the calculatedspectrum is close enough to the spectrum of the pure sodium benzoatepowder. By optimizing the mathematical algorithm in extracting thespectrum of the container, it is possible to further improve the qualityof the obtained spectrum of the sample.

Alternatively, mixture analysis can be performed directly using spectrumin FIG. 6a to identify the material makeup of the sample as a whole,including the container and the content inside. Various mixture spectralanalysis algorithms exist to accomplish such tasks. With prior knowledgeof the container material, the chemical composition of the contentinside can be determined. In yet another implementation, the containerspectrum in FIG. 6b can be designated as a component, and a modifiedmixture analysis method can be used to identify the remaining componentthat make up the spectrum FIG. 6 a.

FIG. 7 illustrates how the light delivery and collection device enablematerial identification by means of Raman spectroscopy through adifferent kind of packaging material, i. e. a brown paper envelope. FIG.7a shows the Raman spectrum of a D(+)-Glucose sample contained in thebrown envelope measured with the aid of a light delivery and collectiondevice as shown in FIG. 1. FIG. 7b shows the Raman spectrum obtainedwithout the device and with the excitation beam focused on the brownenvelope. FIG. 7a shows the Raman spectrum of the D(+)-Glucose sampleobtained without the brown paper envelope. Here the brown envelopespectrum in FIG. 7b displays the signature of cellulose on top of a highlevel of fluorescence. The signature of the glucose content is almostcompletely absent. In contrast, the Raman spectrum obtained with thelight delivery and collection device is almost entirely of D(+)-Glucose,with a relatively weak contribution from the cellulose. In this case,the material inside the packaging material can be directly identified bysearching through a spectral library.

FIG. 8 illustrates how the light delivery and collection device used intransmission mode enables the measurement of bulk material property.Here the sample is an ibuprofen tablet (Advil, 200 mg) purchased from alocal drug store. The tablet has a brown colored coating. The spectrumin FIG. 8a is obtained in transmission mode using the configurationshown in FIG. 4; the spectrum in FIG. 8b is obtained in reflection modeusing the configuration shown in FIG. 1; and the spectrum in FIG. 8c isobtained in reflection mode without the aid of the light delivery andcollection device. The spectrum in FIG. 8c consists of features mostlyfrom the coating of the tablet, while the transmissive Raman spectrum inFIG. 8a consists almost entirely of the drug material inside thecoating. The spectrum in FIG. 8b is similar to the spectrum in FIG. 8a ,but has relatively more contribution from the coating. To those skilledin the art, it is known that the transmission mode measures the Ramansignal throughout the entire thickness of the sample, therefore is moreadvantageous when the bulk property of the sample as a whole is ofinterest.

In the foregoing specification, specific embodiments of the presentinvention have been described. However, one of ordinary skill in the artappreciates that various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofpresent invention. The benefits, advantages, solutions to problems, andany element(s) that may cause any benefit, advantage, or solution tooccur or become more pronounced are not to be construed as a critical,required, or essential features or elements of any or all the claims.The invention is defined solely by the appended claims including anyamendments made during the pendency of this application and allequivalents of those claims as issued.

1. A light delivery and collection device for measuring Raman scatteringfrom an area of a sample, the light delivery and collection devicecomprising: a reflective cavity having a first aperture and a secondaperture, the first aperture is configured to receive excitation lightwhich projects onto the second aperture, the second aperture isconfigured to be applied to the sample such that the reflective cavitysubstantially forms an enclosure covering an area of the sample, whereinthe covered area of the sample scatters the excitation light andgenerates Raman scattered light thereby, and the reflective cavityreflects any excitation light and Raman scattered light scattered fromthe covered area of the sample, except said excitation light and Ramanscattered light that exits the reflective cavity through the firstaperture to be measured, or are re-scattered by the sample at the secondaperture.
 2. The light delivery and collection device of claim 1,further comprising a receptacle configured to receive a probe, whereinthe probe is configured to receive the excitation light from a lightsource and deliver the excitation light through the first aperture intothe reflective cavity.
 3. The light delivery and collection device ofclaim 2, wherein the probe comprises one or more optic components whichfocus the excitation light at the first aperture and thereby deliver theexcitation into the reflective cavity, as well as collect the Ramanscattered light emitted from the first aperture for measurement.
 4. Thelight delivery and collection device of claim 1, further comprising areceptacle configured to receive one or more optical fibers or fiberbundles which terminate at the proximity of the first aperture andthereby deliver the excitation light from a light source into thereflective cavity, as well as collect the Raman scattered light emittedfrom the first aperture for measurement.
 5. The light delivery andcollection device of claim 1, wherein the reflective cavity is made of amaterial having high reflectivity to the excitation light and the Ramanscattered light.
 6. The light delivery and collection device of claim 1,wherein the reflective cavity has a surface coating with highreflectivity to the excitation light and the Raman scattered light. 7.The light delivery and collection device of claim 6, wherein the surfacecoating is a metal coating.
 8. The light delivery and collection deviceof claim 6, wherein the surface coating is a dielectric coating.
 9. Thelight delivery and collection device of claim 1, wherein the reflectivecavity comprises at least one additional aperture.
 10. The lightdelivery and collection device of claim 1, wherein the second apertureof the reflective cavity is at least 2 times as large as the firstaperture in area.
 11. A method for measuring Raman scattering from anarea of a sample, the method comprising the steps of: providing a lightdelivery and collection device having a reflective cavity with a firstaperture and a second aperture; applying the second aperture of thereflective cavity dose to the sample such that the reflective cavitysubstantially forms an enclosure covering an area of the sample;delivering excitation light through the first aperture to be projectedonto the second aperture of the reflective cavity to excite Ramanscattered light from the covered area of the sample, wherein thereflective cavity reflects any excitation light and Raman lightscattered from the covered area of the sample, except said excitationlight and Raman scattered light that exits the reflective cavity throughthe first aperture of the reflective cavity or are re-scattered by thesample at the second aperture; and measuring the Raman scattered lightemitted from the first aperture of the reflective cavity to obtain aRaman spectrum of the sample.
 12. The method of claim 11, wherein thereflective cavity is made of a material having high reflectivity to theexcitation light and the Raman scattered light.
 13. The method of claim11, wherein the reflective cavity has a surface coating with highreflectivity to the excitation light and the Raman scattered light. 14.The method of claim 13, wherein the surface coating is a metal coating.15. The method of claim 13, wherein the surface coating is a dielectriccoating.
 16. The method of claim 11, wherein the second aperture is atleast 2 times as large as the first aperture in area.
 17. A method formeasuring Raman scattering of a diffusely scattering sample having asurface layer and a sub-surface layer of different materials, the methodcomprising the steps of: providing a light delivery and collectiondevice having a reflective cavity with a first aperture and a secondaperture; applying the second aperture of the reflective cavity to thesample such that the reflective cavity substantially forms an enclosurecovering an area of the sample; delivering excitation light through thefirst aperture to be projected onto the second aperture of thereflective cavity to excite Raman scattered light from the covered areaof the sample, wherein the reflective cavity reflects any excitationlight and Raman scattered light scattered from the covered area of thesample, except said excitation light and Raman scattered light thatexits the reflective cavity through the first aperture of the reflectivecavity or are re-scattered by the sample at the second aperture;measuring the Raman scattered light emitted from the first aperture ofthe reflective cavity to obtain a first Raman spectrum of the samplewhich contains signatures of both the surface layer and the sub-surfacelayer of the sample; and removing the light delivery and collectiondevice and focusing the excitation light to the surface layer of thesample to excite Raman scattered light from the surface layer, andmeasuring the Raman scattered light from the surface layer to obtain asecond Raman spectrum of the sample which mainly contains signatures ofthe surface layer of the sample.
 18. A method for measuring Ramanscattering of a transparent or diffusely scattering sample, the methodcomprising the steps of: delivering an excitation light onto a firstside of the sample to generate Raman scattered light; providing a lightcollection device having a reflective cavity with a first aperture and asecond aperture; applying the second aperture of the reflective cavityof the light collection device to a second side of the sample such thatthe reflective cavity of the light collection device substantially formsan enclosure covering an area on the second side of the sample, whereinthe excitation light and the Raman scattered light at least partiallytransmits from the first side to the second side of the sample, and thereflective cavity of the light collection device reflects any excitationlight and Raman scattered light scattered from the sample, except saidexcitation light and Raman scattered light that exits the reflectivecavity through the first aperture of the reflective cavity of the lightcollection device or are re-scattered by the sample; and measuring theRaman scattered light emitted from the first aperture of the reflectivecavity of the light collection device to obtain a Raman spectrum of thesample.
 19. The method of claim 18, wherein the step of delivering anexcitation light onto a first side of the sample to generate Ramanscattered light comprises the steps of: providing the light deliverydevice having the reflective cavity with the first aperture and thesecond aperture; applying the second aperture of the reflective cavityof the light delivery device to the sample such that the reflectivecavity of the light delivery device substantially forms an enclosurecovering an area on a first side of the sample; and deliveringexcitation light through the first aperture to be projected onto thesecond aperture of the reflective cavity of the light delivery device toexcite Raman scattered light from the covered area of the sample,wherein the reflective cavity of the light delivery device reflects anyexcitation light and Raman scattered light scattered from the sample,except said excitation light and Raman scattered light that exits thereflective cavity through the first aperture of the reflective cavity ofthe light delivery device or are re-scattered by the sample.